Not going to say too much here, as I haven't been keeping up with the series, part of which is due to how often lackluster and disappointing S&M was. All I have to say, until I properly catch up with the series and see this episode again, is yeah. . . this ain't the same Mewtwo Ash met in the original series.
I legitimately have to laugh at how the outside word is trying to convince everyone it is more than the story in the actual episode, which doesn't at all. There is not a single reference or recollection of its past events with Ash, something that actually exist in Mewtwo Returns. Both Mewtwo and yes Ash failed to truly convince the audience that they knew each other personally. Majority of the time, as in like practically everytime in this anime, when Ash runs into old friends, humans and Pokemon, there is some sort of background context that comes along with it, whether it's a flashback or unique dialogue, but there was absolutely none here AT ALL. (Of ALL the instances throughout the entire anime series to not have background context, they chose THIS one to have it absent during? Even with all that misleading promotion.) No "long time no see", "you", "it's been a while" and many other variants from any of them two. Ash had already seen a few Mewtwo after Mewtwo Returns, so Ash "recognizing Mewtwo" means nothing, especially with that overrated standard reaction that he's displayed even in normal situations. The reused Movie Mewtwo theme (which is suppose to be outdated since the idea is suppose to be this is the same Mewtwo that Ash had met but also gotten to reform) means nothing too, as well as the return of the original voice actor. (There's still no canonical or personal connection with them two. And even Goh didn't think Ash knew this Mewtwo, yet in contrast he questioned things like his connection with Lugia, Lucario, human characters, etc. Nor did Pikachu do its usual joyful run up that we've seen it do to various returning friends over the many generations.) They put all these together and reaired MSB and MR returns for what, to pull at nostalgia strings/bait views from old watchers and not properly (rather at all) continue their story arc. So yeah, different Mewtwo thanks to the execution of the episode.
Actually, the episode was rather disappointing too. Animation wasn't terrible but it wasn't top notch either. Pikachu went down way too quickly, literally after one real attack. (But this is nothing new with Pikachu. Only decently strong when the plot demands it or when it has to be written exceptionally to negate some of its shortcomings.) The way it lost also reminded me of how it lost to Marshadow, which also irritated me. The Thunderbolt could have resisted the Shadow Ball at least a little. The fact that Aceburn (laughably) and Lucario performed much better is just a problem. Then another thing is Ash basically being scaled to Goh's level during Mewtwo's judgment. Some of the stuff Mewtwo said to Ash insulted me as a veteran follower of the anime. The adventuring segment that came before Mewtwo was mediocre (this is the Pokemon standard, so the praise is questionable), with the Caterpie portion being the only standout thing. There's already been many episodes like this adv-segment, and this one isn't special. Would have been better if there was cooperation between Ash's and Goh's Pokemon, though, especially since that's somewhat the theme for the second half of the episode when they face Mewtwo together.
Frieza-Mewtwo was cool, but I have no idea how this is anyone's favorite episode or somehow in top 5 best Pokemon episodes. If this is somehow the best episode in this series, then i'm even more concerned with catching up. It's also funny how Goh somehow had 7 Pokemon on him, with no onscreen transfers at all. In order he had Mankey, Heracross, Sobble, Caterpie, Krabby, Dewong, and then Aceburn. . . lol.